1. Field of the Invention
The present invention relates to a transmitter and an information processing device performing information transmission through optical communication.
2. Description of the Related Art
In many portable information processing devices such as mobile phones, a plurality of circuits having different source voltages necessary for operation are mounted. For example, a mobile phone operated with a built-in battery includes a control circuit performing information processing, a radio communication circuit, and peripheral circuits of a display, a camera, and the like, which are supplied with individual proper source voltages.
The development of the portable information processing devices is being conducted for the purposes of increasing operating time with the built-in battery or reducing the size and weight using a lower-capacity battery. Accordingly, it is required to reduce the power consumption of the portable information processing devices. It is therefore required to reduce the power consumption of each circuit and reduce the operating voltage of each circuit in the light of ensuring the operational margin for the voltage drop of the battery output.
While the operating voltage of each circuit is being reduced, for example, the operating voltage of a logic operating circuit such as a control circuit has reached 1.5 V or lower, and the operating voltage of an analogue circuit has reached about 2.5 V. In order to supply source voltages necessary for individual circuits, a method is proposed in which a power supply circuit generating various source voltages from the voltage supplied from the built-in battery is mounted on the information processing device.
In data transmission through a comparatively short distance within an information processing device or between information processing devices, in the case of transmitting a large volume of information such as image data, the information transmission is effectively performed through optical communication (hereinafter, referred to as optical transmission) in the light of reduction of electromagnetic interference (EMI), easy layout of transmission lines, and the like. However, the source voltage necessary for a light emitting element used for the optical transmission, such as a semiconductor laser, is about 3.3 V and is generally higher than the source voltage supplied to the other circuits of the information processing device.
It is therefore required to add a power supply circuit for the light emitting element to the information processing device conducting optical transmission. This will increase the manufacturing cost and mounting area of products. Moreover, there is a method of selectively using light emitting element operating at low voltage, but selection of the light emitting element will increase the cost and make it difficult to ensure stable supply thereof.